The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.
Battery packs, for purposes of this disclosure, are series-connected battery elements. These elements may, in turn, include a parallel, series, or combination of both, collection of chargeable energy storage cells, usually rechargeable cells. Collectively all these cells store energy for the battery pack. The series-connected battery elements may, in turn be subdivided into collections of modules, each module including one or more series-connected battery element.
In many instances, the battery pack may be treated as a monolithic unit, providing energy for operation. However, to enable such treatment, individual cells, series-elements, and modules are processed in order to achieve a desired average monolithic effect. One particular concern is that at the individual level, the series elements are not the same and store differing amounts of energy and charge/discharge at different rates. These variations are natural and expected. In certain situations, the variations can lead to an exceptional variation, defined herein as an exceptional charge state, in which an individual series element is excessively overcharged or overdischarged (as compared to some threshold).
Overcharge of a lithium-ion battery can lead to thermal runaway, either directly or via increased susceptibility to abuse due to decreased chemical stability. When charging a battery pack which includes more than one series element, an initial imbalance in the state of charge of the series elements can result in overcharge of one or more of the series elements, even when the voltage of the battery pack does not indicate overcharge. There are conventional solutions to mitigate this potential hazard that monitor series element voltages and are in place to ensure balance prior to charging. However, due to the potential severity of exceptional charge events, particularly for overcharge events, additional systems for identifying series element overcharge in a battery pack before the event becomes severe are desired in the event that the voltage monitoring and balancing system malfunctions or may otherwise insufficiently address the exceptional charge event.
What is needed is a system and method for identifying exceptional charge events of series-connected energy storage elements, and responding appropriately to detected exceptional charge events.